Method and apparatus for ventilating laboratory fume hoods

Abstract

Claims

Feb. 20, 1962 w. w. KENNEDY 3,021,776 METHOD AND APPARATUS FOR VENTILATING LABORATORY FUME HOODS ATTORNEYS Feb. 20, 1962 w. w. KENNEDY METHOD AND APPARATUS FOR VENTILATING LABORATORY FUME HOODS 5 Sheets-Sheet 2 Filed Feb. 19, 1958 INVENTOR. WAL fl? W//ENNE/ BY I 'Mw/fw ATTORNEYS Feb. 20, 1962 w. w. KENNEDY 3,021,776 METHOD AND APPARATUS FOR VENTILATING LABORATORY FUME Rooms Filed Feb. 19, 1958 3 Sheets-Sheet 3 C 0 U 0 O 08000000030 0 0 O O 0 O 000000202020202 @OOO o o@ O O 34 o o o o O O G 0 O o 0 0 0 0 O O 0 O 0 0 O 0 0 o 0 OO 0 -Q 0 000000000 OO 0 00 0 0 O 0 0000000000 OO O O Q O O C O O 000000808 OO GO C O 0000000 o c OO O O O C) 0000808080808 34-f0 0000@ 0 0 0 000000838383838 OO00 0 0 0 0 o o o o O O O O0 0 o 0 0 o o 0 O O O O O o 0 o o O O a. G o 0 o o 0-33 O Q /34 OG O 000000000 O O O/ 0 Ocoooooooo 00 O 0 0 o o o o 00 0 0 O O O O O 000000000" OO Q 0 0 000000000 OO 0 00 0 0 0 0'000000000 O O 0 O 0 0 0 O0 0 000000000 O O O 00000000 O0 ooo O0 0 ogogogooo 33 O0000 0 O O O O O000000000000 OO O O O-Oooogogog/ 00 0 O O O O 33C Q00 O 300000000 OO O O O O O 0000080808383 0000000 0 0 0 pOOOOOgQgOFgOFoOro OOOOO O 0 0 0 /22 f3- l/22a A E 4/` 45 E /33 [/3/ 42` 45 E Q2*L H32 IN VEN TOR. A TTORNE/S icc Patented Feb. 20, 1962 MEmoD 'AND APPARATUS non VENTILATING- LABORATRY FUME HQODS Waiter W. Kennedy, Rockford, Iii., assignor to Barber- Colman Company, Rockford, lll., a corporation of Illinois Filed Feb. 19, 1958, Ser. No. 716,091 4 Claims. (Cl. 98-11S) side`of the areauso' 'as to leave an open face affording access forv the technician. .The hood exhaust-systemv draws in air through the open hood face and thus continuously sweeps the'area of objectionable gases, preventing escape ofthe gasesinto the room. Experience has dictated Ythat the air velocity through the work region should not exceed 100 feet per minute so as not toqblow out 4burner dames, disturb .chemicals of a uiy nature, or aieet the operation of. delicate equipment. .The continuous intake of air by the fumehood and its exhaust. system presents a 'serious problem when the room in which the hood =is located is heated or cooled forthe comfort of laboratory personnel. In a typical hood installation, where the open hoodface measures 32 square feet and the air intake velocity is held at 100 feet per minute, 3200 cubic feet of room air per minute is lost. 'Iosuccessfully air-condition a laboratory having a single hood, an eight-ton unit would be required merely to compensate for the cooled, conditioned air which vis lost.' A . corresponding loss of heated airwould occur in the winter season. In order to avoid this loss while maintaining comfortable conditions for laboratorypersonnel, it has been pro-. posed to introduce unconditioned air from an auxiliary source across vthe open hood face so that the unconditioned air may 'beindrawn through the test area by the hood exhaust system without imposing a drain on the con. ditioned air in the laboratory room. Heretofore, attempts to accomplish this have not been successful. signers have been confronted with the following dilemma: If. auxiliary air is discharged inthe usual fashion from each side of the hood face ata velocity suci'cnt to carry to the center ofthe face, the Vconcentration of air atthis point results in turbulence andan air velocity over the work area far in excessof the desirable 100 feet per minute. If the-velocity of the auxiliary air is reduced, only. the edges of the h ood face are blanketed or curtained by unconditioned air, and the center of thev De-v 2 hood ventilation which not only provides freedomv from .'fumes but which enables thetechnician to work in more comfortable,'even-tempered surroundings .in all seasons of the year. It is an object related to th'e above to provide a method and apparatus of the described character that permits selective operation of any number of fume hoods in a room without requiring adjustment of the vroom air conditioning system in order to maintain room temperature-and secure `a proper air intake velocity across the hoods in operation.- With more particularity, it is an object to provide a fume hood Ventilating apparatus for discharging'a plurality of adjacent, curtain-like air streams across an open hood face' at predetermined relative velocities so that air is supplied without turbulence across the entire open face of the hood, in orderrthat the hood exhaust system may be effectively operated without substantial drawing of air fromthe room in which the fume hood is located. .It is another, more detailed object to provide a fume hood Ventilating method and apparatus as characterized above which develops and discharges a plurality of adjacent -air streams having predetermined vincremental velocities from a common. source/.of static air pressure. It is a related object to provide an apparatus lof this type that is exceptional-ly economical to construct in that no complicated valves or nozzles are relied upon. Y It is a further object to provide a fume hood Ventilating I method and `apparatusreadily adapted -for use with con- FIG. v3 -is a perspective, fragmentaryview, partially broken away, of a portion of the -ventilating structure shown in FIG. l. f FIG. 4 is a fragmentary, horizontal section taken along lineefiin FIG. 1. FIG. '4a is a diagrammatic perspective of the air streams appearing inFIG. 4.Y - FIGS. 5 and 6 show alternate patterns for ,the air valve y. plate shown operably positioned in FIG. "3. " lents as may be included within the spirit and scope of the limited size. It is another object to provide a scheme of IFIG. 72is a section similar to FIG. 4, but showing anA While the invention will be described in connection'A with preferred embodiments and procedures, it will be understood that I do not intend to limit the invention to those embodiments and procedures. On the contrary, I intend to cover all alternatives, modiiications andequivainvention as defined by the appended claims. .'Iurningfnow to the drawings, there is shown a labora-- tory working area in the form of a table top -10 on'which top panel 15 having a downwardly sloping front portion t-he table top and leaves an open hood face 17 which provides access to the working area. For withdrawing objectionable gases from within the hood, au exhaust system 18 is coupled to the hood 11 by an exhaust duct :19 which opens into the hood through the top panel 15. With the exhaust system ,18 in operation, gases Within the hood ylll are continuously withdrawn through the duct 19 and replaced fby air entering through the open hood face 17. v In accordance with the invention, a plurality of adjacent, curtain-like streams-.of air are discharged acrossthe .open hood face v17 from one of its edges, the streams having progressively-varying velocities with the outermost `stream velocity being the highest, so vthat air is uniformly supplied, without turbulence and at low velocities, across the open hood face throughout the flow of the combined air streams. In this way, the exhaust system 18 is prevented from drawing in"conditioned outside air through the open face 17 but is able to control and maintain a steady, low velocity air current over the Vtable top 10. In the present embodiment, three curtain-like streams A, B and C, (see FIGS. 4 and 4a) are discharged across the open hood face 17 Vfrom each opposedlateral edge of the face. The outermost stream C is given a velocity effective to carry the air to approximately the centerline of the table top 10; .the middle stream B is given a velocity sufficient to carryit to the intermediate portion of the hood face, and the rear streamA is given a velocity suii'icient to 'carry only to the side or near Vportion of the face 17. Therefore, each set of curtain-like air streams A, B. and C, completely blankets one-half of the open hood face 17., l Because of theprogressively-varying velocities of the adjacent air streams A, Bland C,- with the outermost stream C being the fastest, it may be seen that each stream provides air to adjacent lateral portions of the` hood face, and therefore the supply of air is substantially uniform over the entire hood face `17. More specifically, each` air stream, A, B landlC, supplies `air directly and without turbulence to the adjacent areas 17a, 17b and 17e of the hood face 17 (FIG. 4a) so that Ythe entirey open face is blanketed.A f vIn a practical case, it will be assumed that an average air velocity over the work area of 100 feet per minute is desired. This'is established by operating the exhaust system 18 so that it moves 10D cubic feet of air for each square foot of open hood face. Under such conditions, and with a work table 6-7 feet long,it has been found' that satisfactory operation results when the air velocity of stream A is approximately 200 feet per minute, the velocity of streamB is approximately 3150 feet per minute and the velocity of stream C. from 600 to 800 feet per minute. The exhaust system 18 will then curve the streamsA, B and C inwardly through the open hood face 17 to create an air intake velocity over the'table 10 of l0() feet per minute.A It` will be understood that `the streams A, B and C curve solely under the influence and controlr of the exhaust system 18. Thus, the initial discharge velocities of the streams merely position the air so that it may be drawn into the hood at the proper velocity by the exhaust system. 1x1-this way, rthe air moves through each of the hood face areas 17a, 1717 and 17e at substantially the same velocity and in the same quantity, i.e. the air tlow uniform across the entirey hood face 17 In order to provide the curtain-like air streams mentioned above, a Ventilating apparatus 20 is utilized having an air supply duct 21, air supply chambers 22 and 23, and an air supply system 24 for maintaining a static air pressure in the chambers 22 and 23. The air supply system 24 feeds air through-'the duct21 and builds up the required dischargeV pressure in the supply chambers 22 and-23. The air supply chambers are provided with opposed,l vertically aligned discharge ports 25 and 26, respectively, and sets of deiiectors 27, 2S (see FIG. 3) areV the air supply chamber 22, by venting equal volumes of' air from the source of static pressure through discharge chambers of progressively-varying width but equal length. Since three streams of air are discharged from the air supply cha-mber k2, three adjacent discharge chambers, 22a, 22b and 22C, are provided, with the outermost `Y chamber 22e being the narrowcst. It will be appreciated that a given volume of air under a constant pressure will flow more rapidly, that is, at a higher speed as measured in feet per second, through a narrow chamber than through a -Wide one, assuming the chambers to be of equal height as in t-he present case, and therefore the discharge velocities of the equal volumes of air vented into the chambers 22a-22e are inversely proportional to the width of the chambers'. By making the discharge chambers of progessively-varying width, with the narrowest at the. outside, the desired air stream velocities are obtained. In the preferred embodiment, the chamberslZa-ZZC rare formed by subdividing a portion of the air supply chamber 22 by positioningwa-ll plates 31, 32 behind the verticalY discharge port 2S land within the chamber 22. In' Yorder to introduce equal volumesof air per unit of time uniformly into cachot the chambers 22a-22o, a valve plate structure 33 is disposed between the discharge members and the air supply chamber 22. Thevalveplate 'structure 33 is provided with diierent patterns of openings permitting equal volumes of air to -flow from the region of staticr pressure within the air supply chamber 22 to the respective air discharge. chambers 22a-22e. In the preferred embodiment, the valve plate 33 is a unitary. structure extending across the chamber 22 and equal volume of air per unit of time will iiowA through the openings in the valve plate yportions 33a-33c under the static pressure in the air supply chamber 22 into the respective air discharge chambers, In order to keep the open areas in each of the valve. plate portions 33o-33e equal when the width of these portions varies, While maintaining uniform` air ow through thelentire plate area, a different pattern of openings is cut into each of the plate portions. In the FIG. , 5 embodiment, the portion 33C is provided with evenly spaced large openings; the portion 33b provided with evenly-spaced intermediate-size openings, while the portionra is provided with a plurality of evenly-spaced openings. By correctly sizing the openings in each of the-plate portionsfan approximately equal amount of open space in each of the plate portions can easily be achieved, with the result that an equal volume of air per minute will flow through the openings in each of the plate-portions. Since'the openings in each plate portion are symmetrically spaced, the How of air therethrough will be substantially uniform. Alternatively, a valve plate 34, made up of plate portions 34a, 341; `and 34e having openings'of equalI size, can be utilized in lieu of the valve plate 33 (see FIG.v 6). The. valve plate`34 is equivalent to the'valveV plate 33 discussed above and may be substituted therefor in the apparatus 20. In order to keep the open area in each-of the valv plate portions Y34a-34e approximately equal, the Iopen-v ings are spaced progressivelyfcloser together, with the openingsfin 34d beingY substantially farther apart than in lthe portion"34c'." In each of the valve plate portions 34a-34e, the openings aresymmetrically located so that the ow of air therethrough will be uniform throughout the plate area. It will be appreciated that by properly spacing theequally sized openings in the respective valve plate portions 34a-34e, Van equalV vopen area `can be achieved in each of the plate portions despite the differences in their width. Thus, a constant volume of air per minute will ow through each of the portions 34a- 34C. In keeping with an alternative aspect of the invention, n charging ports extending from end to end of said hood the pluralty of adjacent curtain-like streams of air A, B and C having progressively-varying velocities may be developed and discharged from a single source of static pressure, that is, the air supply chamber 22, by venting progressively-varying volumes of air from the pressure source through adjacent discharge chambers of substantially equal size (see FIGS. 7 and 8). In this embodiment, parts corresponding to those already discussed have been given identical identifying numerals with the value 100 added thereto. In the alternative embodiment, an air supply chamber 122 is provided with vertically-aligned discharge ports 12S and wall plates 131 and 132 which deline'air discharge chambers 122:1, 122b and 122e. A valve plate 133 is interposed between the air supply chamber 122 and the respective air discharge chambers 122a-122c. As stated above, the air discharge chambersA 12211- 122c are of substantially equal size. To provide a progressive variation in air discharge velocity from the respective chambers, progressively-varying amounts of air are vented through the valve plate 133 into each of the chambers. For this purpose, adjustable venting ports 41, 42 and 43 are provided. Preferably, the venting ports 41-43 have a height substantially equal to the height of the air discharge ports 125, but they are of varying widths so that progressively-increasing volumes of air are admitted to the air discharge chambers 122:2, 122b and 122e, in that order. In order to adjust the width of the Venting ports 41 43, the valve plate 133 is provided with a pair ofk shutterlike doors 45 for each of the ports. It will be apparent that by adjustably swinging these doors about their hinged connections with the valve plate, the effective apertures of the ports 41-43 can be adjusted so that the proper volumes of air will be vented to the air discharge members 122a-122c. In this way, the desired, progressively-variable, air velocities in the curtain-like streams 100a-100c can be easily obtained. I claim as my invention: l. In a laboratory fume hood having an open hoodV face lying in a plane dividing the interior of the hood from the outside room and an air exhaust system for the interior of the hood, a Ventilating apparatus for preventing the air exhaust system from drawing conditioned room air through the plane of the hood face comprising, in combination, an air supply chamber positioned on the room side of said plane and having a wall extending from said plane adjacent one edge of said open hood face, an air supply system for maintaining a static air pressure in Said chamber, said wall having a plurality of adjacent, elongated air discharging ports extendingA face edges and opening into respective ones of said chambers for directing adjacent, curtain-like streams of air from said chambers parallel to said plane and over adjacent portions of the hood face, and m'eans interposed between said chamber and said .ports for causing the air streams discharged from the latter to have progressivelyvarying velocities with the outermost stream from each chamber being the fastest and having a velocity suicient to carrymidway across the hood face so as to meet the opposed outermost air stream, said streams thus blanketing the entire open hood face with uniformly moving air from said supply system. 3. In a laboratory fume hood having an open hood face lying in a plane dividing the interior of the hood from the outside room and an air exhaust system for the interior of the hood, a Ventilating apparatus for preventing theair exhaust system from drawing in conditioned room air through the plane of the hood face comprising, in combination, au` air supply chamber positioned adjagated air discharging ports Aextending from end to end of said hood' face edge and opening into the respective air discharge'chambers for directing adjacent, curtain-like streams of air from said chambers parallel to said plane .'and over a portion of the hood-face, said discharge chambers being of progressively varying widths with the outermost chamber being the narrowest, and means for directing substantially equal amounts of air per unit of time from said supply chamber to each of said discharge chambers so that theair streams discharged from the latter have progressively varying velocities with the outermost stream being the fastest, said streams thus blanketing said hood face portion with uniformly moving air from said supply system. 4. In a laboratory fume hood having au open hood face lying in a plane dividing the interior of the hood from the outside room and an air exhaust system'for the interior of the hood, a Ventilating apparatusfor preventing the air exhaust system fromdrawing in conditioned room air throughthe plane of thejhood face comprising, in combination, an airsupply chamber positioned adjacent one edge of said lopen hood face, an vair supply system for maintaining a static air` pressure in said chamber, a plurality of adjacent, elongated lair discharge chambers positioned on the room side of said plane and having adjacent walls extending-from said plane at one edge of said open hood face, each of said walls having adjacent, elongated air discharging ports extending from end to end of said hood face edge and opening into the respective air discharge chambers for directing adjacent, curtain-like streams of air from said chambers parallel to said plane and over a portion of the hood face, said discharge chambers being of substantial-1y equal size, and means for directing progressively varying amounts of air from said supply chamber to said discharge chambers with the outermost chamber receiving the greatest air volume so that the air streams discharged from Ithe discharge chambers have progressively varying velocities with the outer-

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